Techron.... it's a fuel additive that can be purchased at most any auto parts store, and of course any Chevron Gas station. I've had great results with it as have other members. If you do use it, I would suggest using it in the gas tank BEFORE you change the oil.
Also, as others said, make sure the car is very warmed up... a little hard driving (IE: a few full throttle starts from 1st through 2nd gear, on approved 55 mph road, of course ought to be good enough) to blow out some carbon build-up has been recommended also.

GOOD LUCK!!

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)